Because certain materials damage or wear your nozzles to much the Ruby nozzle was created. This special nozzle with ruby is extremely firm and durable. This nozzle has a diameter of 0.4mm.
Thanks to this special jet nozzle you can print special materials, like nylon or metallike filaments (bronzefill, copperfill, ice-carbon, ...) without problems. The ruby nozzle can be used on different types of 3D printers, depending if you chose the 1.75mm nozzle or the 2.85mm nozzle.